Optic nerve damage reversible?

Almost never: Sometimes you can get lucky, and some of the optic nerve dysfunction is due to swelling, and when the swelling resolves, the vision improves. Thats the theory with ischemic optic neuropathy. But even so, the improvement is marginal.

Depends: On time, severity, etc. Specifically depends if the neurons have died (not recoverable at this time since an extension of the central nervous system) or are just in "distress" and could recover when the inflammation or inciting factor is resolved. Typically, not reversible to normal.

Rarely reversible: Optic nerve damage can happen for a variety of reasons, including vascular causes such as "strokes, " inflammation, compression, and infiltratration. A few of these causes can rarely be reversible with time or interventions, but the exact cause needs to be determined.

Sometimes: Some optic nerve damage is reversible. For example, optic neuritis frequently recovers completely, when the cause is found and can be treated. Optic neuropathy due to vascular disease sometimes recovers. Traumatic injuries of the optic nerve may or may not recover.